Intravascular lithotripsy balloon systems, devices, and methods

Abstract

Various embodiments of systems, methods, and devices are provided for breaking down calcified lesions in anatomical conduits. More specifically, an electrical arc is generated between two spaced apart electrodes disposed within a fluid-filled balloon to generate flow and pressure waves. In some embodiments, the electrodes are spaced apart over a relatively large distance to generate a stronger shock. In some embodiments, ionically conducting saline is constrained between the electrodes to reduce parasitic heating. In some embodiments, the balloon is partially deflated during arc generation.

Description

[Technical field]

[0001] [Inventor] Sam Batchelder, Somers, New York, US citizen John R. Ballard, Waconia, Minnesota, United States citizen Michael P. Brenzel, St. Paul, Minnesota, US citizen Alexander P. Thome, Minneapolis, Minnesota, United States citizen [CROSS REFERENCE TO RELATED APPLICATIONS] This application is a continuation of U.S. Provisional Patent Application No. 63 / 229737, filed on August 5, 2021, and entitled “SYSTEMS, DEVICES AND METHODS FOR GENERATING SUBSONIC PRESSURE WAVES IN INTRAVASCULAR LITHOTRIPSY,” U.S. Utility Patent Application No. 17 / 449883, filed on October 4, 2021, and entitled “SYSTEMS, DEVICES AND METHODS FOR GENERATING SUBSONIC PRESSURE WAVES IN INTRAVASCULAR LITHOTRIPSY,” U.S. Utility Patent Application No. 17 / 449883, filed on November 11, 2021, and entitled “SYSTEMS, DEVICES AND METHODS FOR GENERATING SUBSONIC PRESSURE WAVES IN INTRAVASCULAR LITHOTRIPSY,” No. 17 / 454574, filed on November 11, 2021, entitled “SYSTEMS, DEVICES AND METHODS FOR GENERATING SUBSONIC PRESSURE WAVES IN INTRAVASCULAR LITHOTRIPSY,” and U.S. Utility Patent Application No. 17 / 454587, filed on November 12, 2021, entitled “METHODS, SYSTEMS, DEVICES AND METHODS FOR GENERATING SUBSONIC PRESSURE WAVES IN INTRAVASCULAR LITHOTRIPSY,”No. 17 / 454667, filed on November 12, 2021, entitled “METHODS FOR GENERATING SUBSONIC PRESSURE WAVES IN INTRAVASCULAR LITHOTRIPSY WITH MORE THAN SPARK GAP,” and U.S. Utility Patent Application No. 17 / 454668, filed on November 12, 2021, entitled “SYSTEMS, DEVICES AND METHODS FOR SELECTION OF ARC LOCATION WITHIN A LITHOPLASTY BALLOON SPARK GAP,” No. 17 / 454,718, filed on November 12, 2021, entitled “SYSTEMS, DEVICES AND METHODS FOR MONITORING VOLTAGE AND CURRENT AND CONTROLLING VOLTAGE OF INTRAVASCULAR SUBSONIC LITHOTRIPSY SYSTEMS,” and U.S. Utility Patent Application No. 17 / 454,721, filed on December 14, 2021, entitled “LITHOPLASTY BALLOON SYSTEMS, DEVICES AND METHODS WITH ELECTRODE PAIRS HAVING MULTIPLE SPARK GAP” This application claims the benefit of U.S. Utility Patent Application No. 17 / 644,173, entitled "GAPS (Protein-Based Imaging and Photonics)," which is incorporated herein by reference in its entirety. [STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT] N / A

[0002] The present invention relates to a system, device and method for decomposing calcified lesions in an anatomical conduit, and more particularly, an electrical arc is generated between two spaced apart electrodes disposed within a fluid-filled member to generate flow and pressure waves.

[0003] [Description of Related Art] Various techniques and devices have been developed for use in the removal or treatment of tissue in arteries and similar body passageways, including the removal and / or cracking of calcified lesions formed within the passageway and / or within the walls that define the passageway. A common purpose of such techniques and devices is the removal of atherosclerotic plaques within a patient's arteries. Atherosclerosis is characterized by the buildup of fatty deposits (atheromas) in the intimal layer (i.e., subendothelium) of a patient's blood vessels. Very often, what initially builds up as relatively soft, cholesterol-rich atheromatous material hardens over time, often into calcified atheromatous plaques within the vessel walls. Such atheromas restrict the flow of blood, making the blood vessel less flexible than normal, and are therefore often referred to as stenotic lesions or stenoses, and the obstructing material is referred to as stenotic material. If left untreated, such stenoses can lead to angina, hypertension, myocardial infarction, stroke, and the like.

[0004] Angioplasty, or balloon angioplasty, is an endovascular procedure that widens and treats narrowed or blocked arteries or veins, typically to treat arteriosclerosis. A collapsed balloon is typically threaded through a pre-positioned catheter, over a guidewire, into the narrowed blockage, and then inflated to a fixed pressure. The balloon forces the blockage and surrounding muscle wall within the vessel to expand until the blockage yields due to the radial force exerted by the expanding balloon, opening the vessel with a lumen diameter closer to the native vessel in the area of ​​the blockage, improving blood flow.

[0005] Angioplasty procedures present several risks and complications, including, but not limited to, arterial rupture or other damage to vessel wall tissue from overinflation of the balloon catheter, use of an inappropriately large or stiff balloon, the presence of calcified target vessels, and / or the formation of hematomas or pseudoaneurysms at the insertion site. Typically, pressures produced by conventional balloon angioplasty systems are in the range of 10-15 atm, although sometimes pressures can be higher. As discussed above, a major problem with known angioplasty systems and methods is that occlusion occurs over a relatively short period of time at high stresses and rates of deformation, often resulting in damage or dissection of the conduit, e.g., blood vessel, wall tissue.

[0006] Shockwave Medical Inc markets an alternative to traditional relatively high pressure balloon angioplasty. An example of a prior art intravascular lithotripsy system is shown in FIG. 1, with images taken from Shockwave Medical Inc. U.S. Patent No. 9,072,534. FIG. 1 shows a pulse generator having two insulated conductors, each with a distal end that is stripped from the insulation to form an electrode. As shown, the electrodes are spaced apart to form an electrode pair with a gap between them. Element number 25 shows an arc that occurs between the electrodes when a sufficient voltage is applied to one of the insulated conductors. The electrodes are placed within a fluid filled balloon, generating shock waves that pass through the balloon.

[0007] Known systems developed and marketed by Shockwave Medical require relatively close spacing between the electrodes of an electrode pair and use a relatively large volume of fluid in an inflatable angioplasty balloon to create the desired arc between the relatively closely spaced electrodes while the balloon is in an inflated state creating a pressure of, for example, 4 atm. For these reasons, among others, Shockwave Medical's currently known systems cover a relatively narrow axial extent of the lesion with a single shockwave generator with two spaced electrodes. A typical distance between the spaced electrodes of known systems is about 0.004 in + / - 0.001 in or 0.1 mm. Thus, to cover long lesions, Shockwave Medical's electrode pair structure requires that additional electrode pairs (all of which have a relatively short spacing between the electrodes of the pair of electrodes) be positioned along an elongated carrier and / or a translatable, slidable electrode pair carrier that may be used to translate the electrode pair(s).

[0008] It would be particularly advantageous to provide a system capable of creating a longer arc during arcing to generate more energy than would be generated in a relatively shorter gap between the electrodes. It would be further advantageous to provide a system that maintains a safe temperature of the balloon fluid in response to energizing the electrodes to form a longer current arc across a relatively longer gap.

[0009] Various embodiments of the present invention address these issues, among others, the issues mentioned above. [Brief description of the drawings]

[0010] These drawings are illustrations of particular embodiments and are therefore not intended to limit the disclosure. [Figure 1] 1 shows a prior art system. [Diagram 2] 1 shows a plaque treatment regime in terms of pressure variations over time. [Diagram 3]1 shows the time dependent pressure at the plaque due to an incident shock wave. [Figure 4] 1 shows the sequence of events in which a current pulse through an electrode creates flow and pressure waves. [Diagram 5] Standard timing of current and voltage through the electrodes is shown. [Figure 6] 1 shows a typical sequence of energy production peaks during bubble formation and collapse. [Figure 7A] Two example disks are provided that represent spaced apart electrodes with geometries for electrode and ion current confinement. [Figure 7B] Concentric conducting spheres representing electrodes are provided. [Figure 7C] Spaced apart conductive spheres and associated shapes are provided which represent electrodes. [Figure 8] 1 shows a side cross-sectional view of one embodiment of the present invention. [Figure 9] 1 shows a side cross-sectional view of one embodiment of the present invention. [Figure 10] 1 shows a side cross-sectional view of one embodiment of the present invention. [Figure 11] 1 shows a side cross-sectional view of one embodiment of the present invention. [Figure 12] 1 shows a side cross-sectional view of one embodiment of the present invention. [Figure 13] 1 shows a side perspective cross-sectional view of one embodiment of the present invention; [Figure 14] 1 shows a side perspective cross-sectional view of one embodiment of the present invention; [Figure 15A] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Figure 15B] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Figure 16] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Figure 17] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Figure 18] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Figure 19] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Figure 20]1 shows a cross-sectional view of one embodiment of the present invention. [Figure 21] 1 shows a cross-sectional view of one embodiment of the present invention. [Figure 22] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Figure 23] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Figure 24] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Diagram 25] 1 shows a side cross-sectional view of one embodiment of the present invention. [Figure 26] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Figure 27] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Figure 28] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Figure 29] 1 shows a perspective cross-sectional view of one embodiment of the present invention; [Diagram 30] Figure 30A shows a front perspective view of one embodiment of the present invention, and Figure 30B shows a side perspective view of the embodiment of Figure 32A following corrosion or erosion of a portion of the structure during arcing. [Diagram 31] 1 shows a side cross-sectional view of one embodiment of the present invention. [Diagram 32] 1 shows a side cross-sectional view of one embodiment of the present invention. [Diagram 33] 1 shows a side cross-sectional view of one embodiment of the present invention.

[0011] [Detailed Description of the Invention] A typical and known balloon angioplasty procedure applies hydrostatic pressure (and associated tension) in the range of 1 atm to 20 atm for a period of 0.1 to 100 seconds, which acts to expand the flow path diameter of the blood vessel adjacent to or partially surrounded by the plaque. If the plaque is soft (e.g., not calcified or only partially calcified), this near-static pressure cycle is sufficient for treatment. If the plaque is not soft (e.g., calcified) and extends nearly the entire circumference of the blood vessel, the hoop stress in the plaque generated by this near-static pressure cycle is capable of fracturing the calcification, and this is also sufficient for treatment.

[0012] Plaques that do not respond to the pressure cycles of known angioplasty can be treated with pressure cycles on other time scales that use alternative mechanisms.

[0013] Two regimes are of interest: pressures (and tensions) in the plaque that vary on time scales of 10 microseconds to 10 milliseconds, defined here as flow pulses or flow waves or flows traveling at subsonic speeds, and pressures (and tensions) in the plaque that vary on time scales of 1 nanosecond to 1 microsecond, defined here as pressure waves or shock waves or blast waves or impulses traveling at least the speed of sound. Figure 2 provides graphical examples of time regimes for localized pressure changes. The plaque treatment improvements described below relate generally to the flow and impulse regimes.

[0014] An example of a flow wave or pulse is the displacement wave created in tissue by the contraction of the balloon's surface following a boiling or arcing event in a balloon as is known in the art. As some of the liquid in the balloon vaporizes, its density decreases by a factor of 1000, and the volume occupied by the balloon increases. The bubbles created by current heating using intense ionic currents are vapor pockets that typically expand and contract again in tens to hundreds of microseconds, performing a faster version of a nearly static balloon inflation.

[0015] One example of a pressure or shock wave is the pressure wave created when a blast from an initial arc discharge between electrodes within a balloon impacts saline within the balloon.

[0016] Figure 3 shows a typical example of the localized pressure experienced by an area of ​​tissue surrounding the discharge. The sudden rise in pressure to p+ (pressure phase) followed by a drop below the steady state pressure to p- (tension phase) represents a shock wave. The speed of the shock wave is faster than the speed of sound immediately adjacent to the blast or arc and becomes asymptotic to the speed of sound at greater distances. The tension phase lags behind the pressure phase in time at greater distances from the discharge, such that when the pressure phase becomes asymptotic to the speed of sound, the tension wave travels slightly slower than the speed of sound. Thus, subsonic and sonic waves are generated during balloon lithotripsy.

[0017] The initial shock wave generated by known lithotripsy balloon systems results from a multi-step process 100 having basic steps 10-60 as shown in Figure 4. In the first step 10, two electrodes E1 and E2 in contact with an ionically conductive fluid, saline, have a significant voltage applied between them by an external power source. Shortly after the voltage is applied, a corona discharge is generated from the surfaces of the electrodes and an ionic current flows (as shown by the arrows) through the saline between the electrodes E1 and E2.

[0018] Once the ionic current is established, there is a relatively long period of time, 0.3 microseconds to 1 millisecond depending on the fluid and electrode geometry and voltage, during which the fluid (saline) heats up. Since the current concentration is typically (but not necessarily) highest at electrode E1, E2, the fluid will tend to boil first at electrode E1, E2, as seen in step 20. Since saline is mostly water, the water will spontaneously boil locally at temperatures above 350°C in a sub-microsecond time frame, following the boiling characteristics of other instantaneous boiling systems such as bubble jet printheads. Figure 4 shows a typical case of boiling starting at both electrodes E1, E2 at approximately the same time, and the resulting bubbles growing at approximately the same rate.

[0019] The vapor pocket created by localized boiling spreads quickly due to the high internal pressure initially. Steps 20-40 in Figure 4 show the vapor pocket or bubble spreading and merging into a continuous gas pocket connecting the two electrodes. Leaders, i.e., microscopically thin streamers of ions and electrons in the gas, shown in steps 30-50, can form through the saline vapor connecting the electrodes if there is a continuous gas path between the electrodes and if the pressure, temperature, voltage, and electrode spacing satisfy Paschen's law, i.e., for an electrode distance d e Static pressure p g The voltage V required to initiate dielectric breakdown in a gas B but,

number

[0020] where A and B are constants of the gas composition, and γ se is the secondary electron emission coefficient. In general, a leader can be formed with a sufficiently high electric field strength and a sufficiently low gas pressure. It is less favorable to initiate a discharge in liquid saline because the average time between collisions of ions in the solution is very short, so the acceleration experienced by the ions in the electric field is insufficient to generate additional secondary electrons and ions during subsequent collisions.

[0021] Referring to step 30, when the reader is first created, it is conceptually an ion channel of small radius connecting two electrodes. Electrons flow to the anode and positive ions in the channel flow to the cathode. Although the ion channel has high electrical conductivity, when first created it has a relatively high electrical resistance due to its small radius. Example initial reader resistances for this process are in the kilo-ohm to ohm range.

[0022] The electric field from the voltage applied across the electrodes causes a current to pass through the leader as shown in steps 40 and 50 of FIG. 4. The high current density with the high voltage difference causes the leader to heat up quickly and spread radially as it heats up, which results in a lowering of the resistance of the leader. In approximately 10 nanoseconds to 30 nanoseconds, as in step 40, the resistance of the leader drops to below the series resistance of the conductors in the catheter that carry the driving current from the external pulse generator. Once the leader spreads so that it has a low impedance, most of the current heating created by the current from the generator goes to heating of the electrodes and the conductors in the catheter that are operably connected to a voltage source or power supply.

[0023] Figure 5 shows how the impedance of the leader drops as it develops into an arc, as in step 40 of Figure 3, and the power dissipated into the arc quickly peaks while the voltage and current between the electrodes are both relatively high. Both the current peaks and the voltage drops very quickly, indicating the presence of an arc between the electrodes. The peak in power dissipated into the arc indicates a relatively short time interval during which all of the useful work of heating the growing leader into an arc is done.

[0024] FIG. 6 shows the pressure wave produced by the process described in FIGS. 4 and 5 as pressure over time. The initial pressure intensity peak is a hydrophone measurement of the propagating shock wave, where a bubble forms as energy is delivered to the electrode and a leader through the bubble propagates to the arc. The second pressure intensity peak corresponds to the resulting bubble collapsing, creating a cavitation shock wave. Notably, the initial pressure peak is smaller than the second, or bubble collapse, pressure peak, as indicated by the pressure difference Δ.

[0025] The ability of waves in these regimes to treat plaque is commonly discussed in the art as the stresses to which the plaque is subjected are monotonous. What we currently know about plaque treatment is that one or more of the following processes contribute to varying degrees:

[0026] Yielding or creep of atheromatous material under radial, circumferential, and axial forces produced by near-static balloon inflation up to 1.20 atm.

[0027] 2. Yielding or creep of the atheromatous material under the radial, circumferential, and axial forces created by the balloon's flow displacements which may momentarily exceed the nearly static pressurized displacements.

[0028] 3. Tension and shear forces during the tension stage where shock waves pass through the mineralized material causing crack propagation within the mineralized material.

[0029] 4. Conversion of peak pressures in shock waves to tension by transmission and / or reflection at sites of acoustic incongruity within the plaque (such as the interface between adipose tissue and calcification), which is likely the predominant treatment mechanism.

[0030] 5. Tension, as mentioned above, which upon reflection transforms a peak pressure wave into a peak tension wave, generates cavitation, which then generates a subsequent shock wave due to cavitation collapse, which then propagates additional tension.

[0031] 6. Shock-induced crack expansion by capillary flow into the crack in a manner similar to hydraulic fracturing, which breaks up rock formations for oil extraction.

[0032] 7. A complementary combination of the above effects such as flow events inducing shrinkage and fluid inflow into newly created calcified fissures due to impact events.

[0033] In view of the above mechanisms, optimizing lithotripsy balloon systems and associated treatments and outcomes requires the reconciliation of the following concepts:

[0034] 1. A system that is non-hazardous to the patient and is sufficiently reliable and robust, as is well known in the art.

[0035] 2. A system that is small enough to translate through a near-occluded blood vessel, as is well known in the art.

[0036] 3. A balloon and method of inflating the balloon with saline and an indicator, allowing for a nearly static treatment to be applied and the effectiveness of the treatment to be measured in terms of final opened vessel diameter, as is well known in the art.

[0037] 4. Electrical (or other, e.g. laser or ultrasonic) vapor bubble generation within the balloon coupled with a reduced balloon inflation configuration that allows rapid contraction of the balloon surface and generation of flow waves. This is not known in the art.

[0038] 5. To generate a shock wave with the highest peak pressure and the lowest tension wave pressure, which is consistent with maximizing the electrical energy dissipated when the arc is started and optimizing the length and orientation of the arc, which is not known in the art.

[0039] 6. Locating the source of the shock wave as close as possible to the plaque to reduce the extent to which the peak shock pressure is attenuated by the distance between the source and the plaque. The mechanisms for achieving this as described herein are not known in the art.

[0040] 7. Minimizing thermal heating produced by the treatment. Mechanisms for reducing or minimizing thermal heating that achieve some or all of the above objectives as described herein are not known in the art.

[0041] 8. A delay between treatment pulses allows capillary flow into the cracks created by the previous pulse, speeding up the overall treatment. This is not known in the art.

[0042] It is well known to those skilled in the art that shock waves propagate in the same manner, regardless of the mechanism that generates them. The peak pressure of an intense shock wave at a radial distance r from an initial point source blast is 0 is proportional to the energy of the source and to the inverse cube of the radius from the point source.

number

[0043] Hans Bethe, Klaus Fuchs, Joseph Hirshfelder, John Magee, Rudolph Peierls, and John von Neumann, Blast Wave , Martino Publishing, 2013, p. 49, see equation 2.48.

[0044] At intermediate distances from the source, the shock wave slows down from its initial supersonic speed and the spatial thickness of the wave increases. At these intermediate distances, the pressure dependence is approximately:

[0045]

number

[0046] If the blast source has length L arc and r<3L arc and r If R lies in the plane bisecting the line, then the dependence of the pressure on the range r is:

number

[0047] Cole, Underwater Explosions, Princeton University Press, 1948, pp. 122-7.

[0048] Optimizing the peak pressure experienced by the target plaque involves, i.e., (1) storing as much energy as is practical during the initial period or portion of the discharge, and (2) minimizing the distance between the discharge and the target plaque.

[0049] In this way, the length L arc A linear arc of produces a shock wave whose strength varies with the orientation of the arc. In the axial or longitudinal direction, a linear blast source produces a smaller peak pressure than a point source of equal initial energy, and in the radial direction, the peak pressure is at least L arc In the radial direction, the peak pressure experienced by a plaque at a distance r from the center of the linear arc has the form

number

[0050] In the formula, 0.5≦n≦3. r>>L arc For , n = approx. 1.16. A linear arc behaves like a point source. For very short distances, r < <L arc , n = approx. 1.16. r = approx. L arc For short distances, up to about n = 0.5, the shock wave does not decay as quickly. The longer arcs are oriented to spread preferentially towards the plaque, and it is more efficient to convert the electrical energy associated with the blast into pressure (and tension) effects in at least partially calcified plaque.

[0051] After the arc has stabilized to a low impedance "steady" state, it does not matter to treatment if the continuing voltage pulse is quickly terminated by active control, or if the storage capacitor driving the pulse sags over time as it discharges its stored energy.

[0052] Based on the above understanding of the causal relationships created by the pulse voltage applied to the electrodes, at least the following ideas emerge.

[0053] A. The energy of the shock wave created in a fluid-filled balloon is determined primarily by the energy dissipated in the growth of the leader as it becomes a stable arc. For a fixed distance between the electrodes, the energy dissipated in the growth of the leader to form an arc is determined primarily by the applied voltage, the electrode distance, and the catheter cable impedance. A longer arc can deliver more energy. A longer leader has a higher initial resistance and can convert more of the voltage and current into heat. b. Lower impedance catheter cabling can supply more energy to the leader during its growth phase and can release more energy. c. A higher voltage creates a leader at a higher pressure, which increases the heating rate of the leader, which releases more energy.

[0054] B. Heat dissipated in forming a discharge between the electrodes is dominated by ionic conduction through the saline prior to the formation of a saline vapor path between the electrodes and subsequent Townsend breakdown. Because all paths through the saline fluid connecting the electrodes conduct current in parallel, the paths sampling most of the balloon's saline volume heat up slowly, enhancing tissue heating without contributing to boiling. a. The volume of saline involved in ionic conduction prior to arc formation should preferably be restricted or minimized to the channels connecting the electrodes in the immediate vicinity of the electrodes.

[0055] C. A long arc will preferentially generate shock waves perpendicular to the axis of the arc. To the extent that treatment is performed in the shock regime, it is effective to orient the arc so that the plaque is in that perpendicular direction.

[0056] Furthermore, some of the above embodiments and concepts act to enable others. For example, if the gap between two electrodes in saline is increased, the ionic resistance between the electrodes increases and the average ionic current density between the electrodes decreases. As a result, the amount of energy dissipated by the pulse generator in heating the saline in the balloon to boiling increases nonlinearly with the electrode spacing. To achieve the desired longer arc, it becomes desirable to confine the saline involved in ionic conduction to the small channel connecting the electrodes. In this way, the heating energy required increases only linearly with the gap.

[0057] Achieving a long arc in saline is not as simple as moving the electrodes apart and increasing the voltage. The following example will highlight the problems involved.

[0058] In Figure 7A, two conducting disks, representing example electrodes in a fluid medium of radius a, are separated by d in a medium of conductivity σ. The ionic resistance between the disks is:

number

[0059] In Figure 7B, concentric spheres of radii a and b that are also conducting are separated by a medium of conductivity σ. The ionic resistance between the spheres is:

number

[0060] The resistance of a hemispherical electrode of radius b in a balloon of radius a separated by a distance c = d + 2(ab) is

[0061] As shown in FIG. 7C, R disks and 4R spheres (Because the current only passes through half the "sphere" at each electrode, the resistance there is doubled, and this occurs at both electrodes).

number

[0062] The volume of a medium of conductivity σ that carries electric current is:

number

[0063] Voltage V applied between the electrodes 0 is the power V 0 2 / R electrodes If a medium has heat capacity Cp and density ρ, then the average rate of temperature rise of the medium is:

number

[0064] Consider three limiting case geometries for the example in FIG. 7C. In the first case, a is large compared to the electrode radius b. If the electrode separation is also smaller than a, the heating rate in this unconstrained case is

number

number

[0065] In the second case, a-b, the medium is confined to a cylinder between the electrodes of area approximately the same as the electrodes and perpendicular to the flow of current. In this constrained case, the heating rate is

number

number

[0066] The average restraint case is 4a 3 / (3bd 2 ) heats up twice as fast. The restraining case is BD / A 2 For example, a constrained case of electrodes of radius b = 0.05 mm spaced d = 0.5 mm apart, with current passing through a fluid channel between them also of radius 0.05 mm, heats the fluid on average 6,800 times faster while using 0.2% of the power compared to an unconstrained case where a balloon of inner radius a = 4 mm limits the ionic current from electrodes of the same size and spacing.

[0067] The third limiting case is when the distance between the electrodes approaches the diameter of the electrodes, in which the current concentration regions near the electrode surfaces overlap, resulting in a thermal efficiency intermediate between the constrained and unconstrained cases.

[0068] The benefits of a constrained or limited ion current channel, which in turn leads to a longer arc between the electrodes, are not apparent when considering prior art designs, primarily because the arc lengths of these designs are shorter.

[0069] To reduce the amount of heat dissipated into the saline solution during the boiling phase, the ionic current should be confined to the greatest extent possible in the narrow channel connecting the electrodes. This also reduces the proportion of energy stored at high voltage in the power supply that is wasted in heating rather than generating an arc.

[0070] The partial collapse of the balloon around the electrode pair(s) acts to form a narrow channel of fluid between the spaced apart electrodes in the electrode pair. Other mechanisms for confining or restricting fluid around the electrodes are described below.

[0071] Long arcs (longer than about 0.5 mm) are impractical within an inflated balloon without some additional mechanism to limit the volume of saline accessible to the ionic current, because the rate of heating generally increases linearly with the conductivity of the saline, and generating long arcs without appropriate fluid restriction measures can result in harmful overheating of the fluid during treatment.

[0072] As one skilled in the art will now realize, restricting or confining the fluid to a smaller, narrower channel or volume around or between the electrodes is a technique that can be implemented and allows for longer arcs (longer than about 0.5 mm) and / or shorter arcs, i.e., less than 0.5 mm, with safe levels of heat generation. The following embodiments will have beneficial effects for gaps between spaced apart electrodes and arcs generated therebetween having lengths between 0.1 mm and 15 mm.

[0073] 8 provides an example of an example flow and pressure wave generator comprising two spaced apart electrodes E1, E2 disposed within a fluid restricting or constraining structure, shown as an example sleeve 300, that provides a narrow channel for fluid F between electrodes E1 and E2. An elongate catheter or member 302 has two example electrodes E1, E2 housed within a sleeve that may be constructed of a polymer, e.g., silicone. The sleeve, in turn, is sealed to form a watertight interior when at least partially inflated, and may be enclosed within an inflatable balloon 304 comprising a fluid F, e.g., saline, the inflatable balloon 304 comprising multiple inflatable configurations, each inflatable configuration having a different fluid pressure. Each inflatable configuration of the inflatable balloon 304 has a volume greater than the volume of the sleeve 300. The inflatable balloon 300 may be in fluid communication with a fluid channel via a fluid supply line disposed in or along the elongate catheter or member 302, which is in communication at its proximal end with a fluid reservoir for inflating or deflating the inflatable balloon through an opening (which may be valved) in the catheter within the interior of the inflatable balloon, and is in fluid communication with the fluid reservoir via the fluid supply line and fluid channel.

[0074] The sleeve 300 may be expandable, but has a maximum inflated diameter that is smaller than the diameter of the expandable balloon 304 such that the sleeve 300 in the expanded configuration narrowly limits the amount of volume of fluid between the electrodes El and E2 relative to the amount or volume of fluid in the balloon. In some embodiments, the maximum inflated diameter of the sleeve 300 is no more than two times the maximum inflated diameter of the balloon 304. In other embodiments, the maximum inflated diameter of the sleeve 300 is no more than three times the maximum inflated diameter of the balloon 304. In other embodiments, the maximum inflated diameter of the sleeve 300 is no more than five times the maximum inflated diameter of the balloon 304. In other embodiments, the maximum inflated diameter of the sleeve 300 is no more than ten times the maximum inflated diameter of the balloon 304.

[0075] Additionally, the expansion volume of sleeve 300 is less than the expansion volume of balloon 304. In some embodiments, the maximum expansion volume of sleeve 300 is less than or equal to two times the maximum expansion volume of balloon 304. In other embodiments, the maximum expansion volume of sleeve 300 is less than or equal to three times the maximum expansion volume of balloon 304. In other embodiments, the maximum expansion volume of sleeve 300 is less than or equal to five times the maximum expansion volume of balloon 304. In other embodiments, the maximum expansion volume of sleeve 300 is less than or equal to ten times the maximum expansion volume of balloon 304. In other embodiments, the maximum expansion volume of balloon 304 is greater than or equal to 1.5 times the maximum expansion volume of sleeve 300.

[0076] The diameter of the example elongate catheter or member 302 may be 1.5 mm (0.20-0.40 in), the radial thickness of the example electrodes E1, E2 may be 0.2 mm (8 mils) (0.002-0.004 in), and the thickness of the example sleeve 300 may be 0.05 mm (2 mils) (0.0005-0.003 in). Other thicknesses may be used and are within the scope of the disclosure and inventions described herein. There are conductive wires connecting the electrodes E1, E2 to a power supply or voltage pulse generator, not shown, but known to those skilled in the art, for example, as described herein.

[0077] Optional laser cut slot(s) or groove(s) 306 are shown disposed within the interior of the sleeve 300 along the elongate catheter or member 302. This optional slot or groove 306 acts in its closed or neutral state to isolate the ionic current within the sleeve. Once a boiling event is initiated, the increase in pressure within the sleeve opens the slot, allowing non-destructive flow out of the sleeve. Between events, saline refills the interior of the sleeve. The response of this embodiment follows the resistance and time response of the constrained case calculated above.

[0078] The example sleeve 300 of FIG. 8 at least partially surrounds the elongate catheter or member 302 and includes a proximal end and a distal end that are at least partially in fluid communication with the fluid F of the encapsulating balloon when in an inflated configuration. This allows the fluid of the encapsulating balloon to enter the example sleeve and provide the fluid F into the gap between the two electrodes. Portions of the proximal and / or distal ends of the sleeve 300 may be glued and / or fastened to the catheter or member 302 to secure the sleeve 300 in place around the insulated portions of the electrodes El, E2, spaced apart from the non-insulated portions of the electrodes El, E2. Alternatively, portions of the sleeve 300 may be glued to the insulated portions of one or both of the electrodes El, E2. Preferably, the sleeve 300 includes silicone that may be placed around the electrodes El, E2 as shown. Fluid F may be permitted to travel from the encapsulating balloon, for example, through one or more flow channels provided between the elongate catheter or member 302 and the proximal and / or distal ends of the sleeve, into the sleeve, and into the gap between electrodes El and E2 via fluid connection to the proximal and / or distal ends of the sleeve 300. The flow channels may be separately defined structures, such as tubes or conduits, as a result of the inner surfaces of the proximal and distal ends of the sleeve 300 being spaced from the outer surface of the elongate catheter or member 302.

[0079] Applicant has discovered that the sleeve 300 may be disposed on or along the exterior surface of the flow and pressure wave generator described herein, and arcing between spaced apart electrodes of the flow and pressure wave generator will not adversely affect or damage the sleeve 300. In some embodiments, the sleeve 300 may be placed along the surface of the spaced apart electrodes of the flow and pressure wave generator described below. These embodiments of the sleeve 300 are applicable to all flow and pressure wave generator embodiments described herein, and preferably the sleeve 300 comprises silicone.

[0080] In some embodiments, the sleeve 300 may be sealed at the proximal and distal ends and suitable for either active or passive fluid inflow. In passively filled sleeve 300 embodiments, one or more openings, slits, holes, etc. may be provided at one or more points along the sleeve 300 to allow fluid to flow from the encapsulating balloon into the interior of the sleeve 300.

[0081] In an alternative embodiment, the sleeve 300 may be in fluid communication with a fluid channel disposed in a central catheter, the fluid channel being in fluid communication with a fluid reservoir at its proximal end. An opening, which may be valved, may be provided in the sleeve and through the catheter and in fluid communication with the fluid channel and the interior of the sleeve 300. The fluid channel may be a separate sleeve fluid channel or a common fluid channel used for both the sleeve and the inflatable balloon. Alternatively, the fluid channel may ride on the exterior surface of the catheter or member 302, and the balloon is sealed around the fluid channel and the exterior surface of the catheter. This active inflation and deflation mechanism is well known to those skilled in the art and has been described above in connection with the inflatable balloon 304, but is not shown.

[0082] In yet another alternative embodiment, the encapsulating inflatable balloon 304 may not be required or provided such that the sleeve 300 provides a desired narrow channel for fluid F between electrodes E1 and E2 while the expansion and contraction of the sleeve 300 is achieved by the fluid reservoir, fluid channels, and opening flow paths described above.

[0083] Turning to FIG. 9, an example intravascular lithotripsy device 350 is provided. An elongated catheter or member 302 is provided with an encapsulation balloon 304 disposed about the catheter or member 302 to define a balloon interior that can be inflated and / or deflated with a fluid F, such as saline, such that the balloon 304 is sealed at both the proximal and distal ends. Two flow and pressure wave generators 352, 353 with spaced apart electrodes (the structures of which are described further below) are disposed along the elongated catheter or member 352 in axially spaced apart relationship to one another. The flow and pressure wave generators 356 and 357 are electrically connected by one or more wire conductors W and with a voltage pulse generator (not shown). Each flow and pressure wave generator 356, 357 is surrounded by an example sleeve 300, which is described in various embodiments in connection with FIG. 10. As also described in FIG. 10, the encapsulation balloon 304 surrounds the sleeve 300 and the flow and pressure wave generators 356, 357. The fluid reservoir is shown in fluid communication with the interior of the balloon 304 through a fluid supply line and fluid openings.

[0084] As noted above, if a partially collapsed balloon is used to confine ionic current by providing a narrow fluid channel between the electrodes, it is preferable to limit the movement or position of the balloon to create a protective distance between the balloon when an arc is formed.

[0085] FIG. 10 shows a partial sleeve 360 ​​with standoffs 362 covering each electrode E1, E2 and limiting the distance of the inflated configuration of the partially collapsed balloon to each electrode E1, E2 and any resultant arcing between them. The standoffs 362 are shown in annular shape and are located at the open end of each partial sleeve 360 ​​with a diameter larger than that of the associated electrode, the standoffs 362 being located axially spaced from the associated electrode and in the gap between the two electrodes E1 and E2. The standoffs 362 may be constructed in any shape as long as the previous element is satisfied. In this way, the standoffs 362 and the partial sleeve 360 ​​create a barrier to the electrodes E1, E2 and resultant arcing in the partially collapsed balloon. The partial sleeve 360 ​​may be attached to the insulating portion of the catheter or elongate member 302 and / or its respective electrodes E1, E2 to maintain it in place.

[0086] 8 and 9 to ensure that the sleeve 300 is held at a safe distance from the uninsulated electrodes and the electrical arc generated between them. In these embodiments, the standoffs 362 may be connected to the interior of the sleeve 300 or to the exterior surface of the elongate catheter or member 302. The partial sleeve 360 ​​is surrounded by an encapsulating inflatable balloon 304 whose interior is in fluid communication with a fluid reservoir via fluid supply lines, fluid channels, and openings disposed through the catheter or member 302 and within the balloon.

[0087] FIG. 11 illustrates an embodiment of a flow and pressure wave generator 400. The flow and pressure wave generator 400 comprises a support or body portion 402 that is electrically conductive but is primarily covered with an insulating material I. The support portion 402 may be attached to the elongate catheter or member 302. The support portion 402 comprises a notch portion 404 and a channel 406 in communication with the notch portion 404. The channel 406 allows a wire conductor W to extend along the support portion 402 and the notch portion 404, and provides a fixed receiving structure for the wire conductor W that is connected to a voltage pulse generator (not shown but described herein). A return conductor WR is also shown for connection to the voltage pulse generator to complete the circuit.

[0088] The wire conductor W is primarily covered by insulation, with the wire free of insulation exposed, and includes a stripped portion disposed within the cutout 404 and proximal to the distal-most end of the stripped portion. The distal-most insulation portion of the wire conductor W and a portion of the insulated wire conductor proximal to the stripped portion are both received within channels 406 on opposite sides of the cutout 404. The stripped portion defines a first electrode 410 of the flow and pressure wave generator 400.

[0089] The embodiment of cutout 404 shown includes two arcuate or convex structures not covered by insulation on opposite sides of cutout 404. The two arcuate or convex structures respectively define a second electrode 411 and a third electrode 412 within flow and pressure wave generator 400. Electrode 410 is radially spaced from electrode 411 and also radially spaced on the opposite side from electrode 412, resulting in a gap therebetween.

[0090] The first, second and third electrodes 410, 411 and 412 are preferably all at the same radial location relative to the outer surface of the catheter member 302. In other words, the location and / or placement of the electrodes 410, 411 and 412 are preferably the same diameter.

[0091] In other embodiments, one or more of the electrodes 410, 411, 412 may be at a different radial location, i.e., not at the same diameter as the other electrodes. In these embodiments, one or more of the electrodes 410, 411, 412 may be disposed radially below or radially above the other electrode(s) 410, 411, 412.

[0092] As shown, the flow and pressure wave generator 400 has two arc-generating regions, as illustrated by arc 414 between electrodes 410 and 412 and arc 416 between electrodes 410 and 411, that exist when a voltage pulse generator (not shown but described above) supplies sufficient voltage to the first electrode 410.

[0093] The activated arc generating regions 414,416 may be influenced by the relative sizes or surface areas of the arcuate electrodes 411,412 and / or the relative sizes of the gaps between the first electrode 410 and the second and third electrodes 411,412.

[0094] The surface areas of the electrodes 410, 411, and 412 may be substantially equal. In other embodiments, one or more of the electrodes 410, 411, and 412 may have unequal surface areas, for example, one or two electrodes may have a larger surface area than the other electrodes.

[0095] As shown in FIG. 12, an alternative flow and pressure wave generator 400' is shown, which is an improved version of the flow and pressure wave generator of 400. The flow and pressure wave generator 400' comprises a support 402' that is electrically conductive but is primarily covered with an insulating material I. The support 402' may be attached to the elongate catheter or member 302. The support 402' comprises a notch 404' and a channel 406' in communication with the notch 404'. The channel 406' allows the wire conductor W to extend along the support 402' and the notch 404' and provides a fixed receiving structure for the wire conductor W to be connected to a voltage pulse generator (not shown, but described herein). A return conductor WR is also shown for connection to the voltage pulse generator to complete the circuit.

[0096] The wire conductor W is primarily covered by insulation and lacks insulation with exposed wire, and includes a stripped portion disposed within the cutout 404 and proximal to a distal-most end of the stripped portion. The distal-most insulation portion of the wire conductor W and a portion of the insulated wire conductor proximal to the stripped portion are both received within channels 406 on opposite sides of the cutout 404. The stripped portion defines a first electrode 410 of the flow and pressure wave generator 400.

[0097] 14 includes a single arcuate or convex structure that is not covered by insulation on one side of the cutout 404'. The arcuate or convex structure defines a second electrode 412' that is radially spaced from the electrode 410, thereby creating a gap therebetween.

[0098] Both the first and second electrodes 410 and 412' are preferably at the same radial location relative to the outer surface of the catheter member 302. In other words, the location and / or placement of the electrodes 410 and 412' are preferably at the same diameter.

[0099] In other embodiments, one electrode 410 and 412' may be at a different radial location from the other electrode, i.e., the electrodes 410 and 412' may not be at the same diameter. In these embodiments, one or more of the electrodes 410 or 412' may be disposed radially below or radially above the other electrode(s) 410 or 412'.

[0100] As shown, the flow and pressure wave generator 400' may have one arc generation region as illustrated by the arc 414' between electrode 410 and electrode 412' that exists when a voltage pulse generator (not shown but described above) supplies sufficient voltage to the first electrode 410. Alternatively, a third electrode 411' may be provided along the flat region as shown, so that this embodiment comprises two arc generation regions.

[0101] The surface areas of the electrodes 410 and 412' may be substantially equal. In other embodiments, one or more of the electrodes 410 and 412' may have unequal surface areas, for example, one or two electrodes may have a larger surface area than the other electrode.

[0102] 11 and 12, respectively, the arcuate or convex shape of the electrodes defined by the cutouts 404, 404' is merely exemplary, other shapes may be used and will occur to those skilled in the art, all of which are within the scope of the present embodiments.

[0103] Turning to Fig. 13, the example flow and pressure wave generators 400, 400' of Figs. 11 and 12 may be disposed within a fluid-restricting sleeve 300, as described in connection with Figs. 8 and 9, to obtain the benefits associated with the longer arcs described. This example embodiment of a fluid-restricting device does not require an encapsulating balloon, as the sleeve 300 is sealed to provide a water-tight enclosure for the fluid, as shown in Fig. 13 and described above. The sleeve 300 may be pre-filled prior to insertion into the subject's vessel, or may be actively filled using fluid channels through or along the elongated catheter or member 302, with the sleeve 300 in fluid communication with a fluid reservoir (not shown, but also known in the art and described herein).

[0104] Therefore, all flow and pressure wave generators may include embodiments having a sleeve 300 to confine the fluid to a narrow channel between the electrode pairs as described herein, and may or may not require a confining balloon.

[0105] 14 illustrates an alternative embodiment of a flow and pressure wave generator 500 similar to that of the flow and pressure wave generator 400, but having first and second cutouts 404, 405 formed or defined in the support 402, the cutouts 404, 405 being radially spaced apart from one another. Each of the first and second cutouts 404, 405 may include a first electrode 410 and second and third electrodes 411 and 412 as shown and as described in connection with FIG. 11. Each conductor W, WR is connected to a voltage pulse generator as shown.

[0106] An example of current flow for the apparatus of Figure 14 is now provided. Initially, a voltage pulse of sufficient strength is sent from a voltage pulse generator through a wire conductor W to generate an arc 414 between a first electrode 410 and, for example, a third electrode 412. The initial arc 414 is generated in the first notch 404.

[0107] After an initial arc 414 is created between the first and third electrodes 411, 412 at the first cutout 404, current flows through the conductive support member 402 to the second cutout 405, which has the same electrode configuration as the cutout 404. In this manner, current may flow from the conductive support member 402 to the third electrode 412 in the second cutout 405 (as shown) and an arc 414' may be created between the third electrode 412 in the second cutout 405 and the first electrode 410.

[0108] Alternatively, if an initial arc 415 is created between the first electrode 410 and the second electrode 411 at the first cutout 404, the current flow may be reversed around the support element 402. In this case, the current would flow from the second electrode 411 through the conductive support 402 to the second electrode 411 in the second cutout 405. An arc 415' may be created between the second electrode 411 in the second cutout and the first electrode 410.

[0109] In both cases, once the second arc, either 414' or 415', is generated, current flows through the return wire conductor WR to the low power or ground side of the voltage pulse generator as shown.

[0110] There are also channels 406 defined in the support 402 to receive the wire conductor W and wire return conductor WR and associated stripped and exposed portions (forming the first electrode 410). In this manner, radially spaced arcs and resultant pressure waves may be generated within a single flow and pressure wave generator. These channels 406, if present in any of the embodiments described herein, help to reduce crossing profiles.

[0111] 14 shows first and second cutouts 404 and 405 at substantially diametrically opposed radial locations, i.e., approximately 180 degrees radially spaced apart. This is merely an example and alternative radial spacings may be provided. In addition, more than one cutout or two or more cutouts may be provided with associated electrode pairs, such as electrodes 410, 411, and 412. Thus, for example, two, three or more cutouts may be provided to create pressure waves, for example, from radial locations 120 degrees apart from each other around the support 402.

[0112] Turning to Figures 15A and 15B, an alternative flow and pressure wave generator 600 is provided, in which the support 402 defines a first notch 602 and a second notch 603. As mentioned above, the support 402 is conductive but insulated except for two non-insulated portions that define the second electrode 411 and the third electrode 412, which elements are also described above. An insulated wire conductor W, which is connected to the high power side of the voltage pulse generator, is disposed in the first notch 602 and extends through the channel 106 in fluid communication with the first notch 602, with a stripped portion defining the first electrode 411 as described herein. The first electrode 410 is radially spaced from the second and third electrodes 411, 412 and lies in the same radial plane as the second and third electrodes 411, 412 creating a gap therebetween. The distal end of the insulated wire conductor terminates in a distal portion of the channel 405 of the first cutout 603 .

[0113] The second cutout 603 has the same structure as the first cutout 602, except that the wire conductor W is insulated and comprises a second wire having a stripped exposed or uninsulated portion that defines the first electrode 410 of the second cutout 602, with a proximal insulated end of the second insulated wire conductor terminating in a proximal portion of the channel 406 of the second cutout 603. The second cutout 603 also has a portion that is uninsulated to define second and third electrodes 411, 412 and that extends toward the first electrode 410 of the second cutout 603. The first electrode 410 of the second cutout 603 is radially spaced from and coaxial with the second and third electrodes 411, 412 of the second cutout 603.

[0114] The flow and pressure wave generator 600 is thus configured to house one or more of the supports having a notch and a defined electrode pair as described and shown in FIG. 17A. The second insulated wire conductor W2 may simply return to the low power side of the voltage pulse generator. Alternatively, the second insulated wire conductor W2 may connect to another support having a notch and a defined electrode pair in series connection.

[0115] FIG. 15B shows such a series connection comprising a first proximal support portion 402 having first and second cutout portions 602, 603 and first, second and third electrodes 410, 411, 412 disposed and / or defined by or within the cutout portions 602, 603, respectively, and a second distal support portion 402 having first and second cutout portions 602, 603 and first, second and third electrodes 410, 411, 412 disposed and / or defined by or within the cutout portions 602, 603, respectively.

[0116] 15A, for each of the supports 402 connected in series, an arc generated between the first electrode 410 and the second electrode 411 of the first cutout 602 is represented as 415, and an arc generated between the first electrode 410 and the third electrode 412 of the first cutout 602 is represented as 414. Then, for each of the supports 402 connected in series, an arc generated between the first electrode 410 and the second electrode 411 of the second cutout 603 is represented as 415', and an arc generated between the first electrode 410 and the third electrode 412 of the second cutout 603 is represented as 414'.

[0117] The current flow in Figure 15A is the same as that described in connection with Figure 16. The current flow in Figure 15B may proceed as follows: First, a voltage pulse of sufficient strength is sent from a voltage pulse generator through a wire conductor W to generate an arc 414 between a first electrode 410 and, for example, a second electrode 411. An initial arc 415 is created at a first notched portion 602 in the proximal or first support portion 402.

[0118] After an initial arc 415 is created between the first electrode 410 and the second electrode 411 at the first cutout 602, current flows through the conductive support member 402 to the second cutout 603, which has the same electrode configuration as the first cutout 603. In this manner, current flows from the conductive support member 402 to the second electrode 412 in the second cutout 603 (as shown) and an arc 415′ may be created between the first electrode 410 and the second electrode 411 in the second cutout 603 of the first or proximal support member 402.

[0119] The first electrode 410 in the second notch 603 of the first or proximal support 402 comprises a conductive insulated wire W2 operably engaged to the first notch 602 of the second or distal support 402. Current may thus flow from the first electrode 410 in the first notch 602 to the third electrode 412 in the first notch 602 and may generate an arc therebetween. The current may then flow through the second or distal support 402 to the second electrode 411 in the second notch 603 of the distal support 402 and an arc may be generated between the second electrode 411 in the second notch 603 and the second or distal support 402 and the first electrode 411. The first electrode 411 in the second notch 603 also functions as a return conductive wire WR and connects to a voltage pulse generator to complete the circuit.

[0120] Each of the flow and pressure wave generators 600 can thus generate one or more than one arc and resultant pressure wave per sufficient voltage pulse. In the case illustrated in FIG. 15B, the proximal and distal flow and pressure wave generators 600 would each generate two successive, radially separated arcs and pressure waves per sufficient voltage pulse. In addition, the pressure waves generated by the two flow and pressure wave generators would be axially or longitudinally separated.

[0121] FIG. 16 is a cross-sectional view of the flow and pressure wave generator of FIGS. 15A and 15B, further illustrating an embodiment in which electrodes 410 , 411 , and 412 are all positioned about the same diameter around support 402 .

[0122] 17 and 18 show the flow and pressure wave generator of FIGS. 15A and 15B, with the individual flow and pressure wave generators 600 housed within a single sleeve 300, as described above. In alternative embodiments, a single sleeve 300 may be used to enclose each of the individual flow and pressure wave generators 600. The sleeve(s) 300 may be used with or without an encapsulating balloon, as described above, and may be actively or passively inflated or deflated. As shown, the interior of the sleeve 300 is in fluid communication with a fluid reservoir via fluid supply lines, fluid channels, and openings through a catheter or member 302 provided within the interior of the sleeve 300.

[0123] 19 is another embodiment of a flow and pressure wave generator 700, similar to the embodiment described above, except that the cutouts do not include uninsulated arcuate or convex structures to form electrodes. Instead, at least a portion of the edge of the body of the support 402 that defines the cutouts is uninsulated. A single cutout, such as 420 as shown, or radially spaced cutouts 420, 421 as shown may be provided.

[0124] The flow and pressure wave generator 700 comprises a support 418 that is electrically conductive but is primarily covered with an insulating material I. The support 418 may be attached to an elongate catheter or member (not shown but described herein). The support 418 comprises a first notch 420 and a second notch 421 that are substantially identical in shape, and a first channel 406 and a second channel 407 that communicate with the notch 404'. The channel 406 allows a wire conductor W to extend along the support 418 and the first notch 420, and the channel 407 allows a wire return conductor WR to extend along the support 418 and the second notch 421. Each channel 406, 407 provides a fixed receiving structure for a wire conductor W, WR, respectively, either of which is connected to a voltage pulse generator (not shown but described herein).

[0125] Those skilled in the art will appreciate that the WR may indeed return directly to the voltage pulse generator to complete the circuit, but will also readily appreciate that the WR may also lead to other flow and pressure wave generators 600 remote from the first flow and pressure wave generator, where the flow and pressure wave generators are arranged in a series electrical connection, similar to the electrical configuration of Figure 17B, with the wire conductor returning to the voltage pulse generator after the last flow and pressure wave generator 600 in a series of two or more flow and pressure wave generators 600.

[0126] The wire conductors W, WR are each primarily covered by insulation and have exposed wire, with stripped portions lacking insulation disposed within the first cutout 420 (W) and second cutout 421 (WR), as described herein, with the exposed wire disposed between the insulated portions of the wire conductors W, WR. The portions of the insulated wire conductor W proximal and distal to the stripped portions are both received within channels 406 defined along opposing sides of the cutout 420. Similarly, the portions of the insulated wire conductor WR proximal and distal to the stripped portions are both received within channels 407 defined along opposing sides of the cutout 421. The stripped electrodes 425 define first electrodes within the first cutout 420 and second cutout 421, respectively.

[0127] The first cutout 420 includes at least one non-insulated region along an edge E of the cutout 420 that at least defines a second spaced apart electrode 423 to the first electrode 410 with a gap therebetween. A second non-insulated region may be formed on the opposite side of the cutout by removing insulation from the edge of the cutout 420, thereby defining a third spaced apart electrode 425 to the first electrode 410 with a gap therebetween.

[0128] The second cutout portion 421 may have the same structural features as the first cutout portion 420 .

[0129] All of the electrodes 410, 423, 425 of the flow and pressure wave generator 700 are preferably of the same diameter, although one or more of the electrodes may not be of the same diameter as the other electrodes.

[0130] Turning now to Figures 20 and 21, a cross section is cut through an exemplary flow and pressure wave generator to show an example of material configuration and hierarchical structure.

[0131] Parts A and C are the anode / cathode core elements.

[0132] B is an insulating layer of component A.

[0133] D is an insulating layer of component C.

[0134] 21, members A and C each include a peeled portion defining a first electrode 410 disposed in spaced apart relationship with a second electrode 411 and a third electrode 412, as described herein. Each of members A and C and the associated second and third electrodes 411, 412 are disposed within first and second cutouts, as described herein.

[0135] E is the anode / cathode core element.

[0136] F is an insulating layer of member E made of polyimide or the like that can withstand high temperatures.

[0137] G is the anode / cathode core element and is a discontinuous conductive support sleeve member.

[0138] H is a support member, for example a long catheter or member 302 made up of three elements, I, J, and K.

[0139] The IN is an inner layer of the support member that is constructed of an electrically insulating material that is low friction to facilitate movement over the guidewire.

[0140] J is a middle layer of support member comprised of mechanical support properties such as a braid or coil.

[0141] K is the outer layer of the support member made of an electrically insulating material capable of withstanding high temperatures, such as polyimide.

[0142] L is a ground wire that extends to another non-continuous conductive support sleeve member and is not attached to member G.

[0143] The lumen is defined as shown to receive an elongate catheter or member 302 as described herein.

[0144] In general, embodiments of the present invention comprise methods and apparatus for generating flow and pressure waves traveling at subsonic and sonic and / or supersonic speeds to disrupt or crack calcified regions within a blood vessel, although the disruptive effects of the generated flow and pressure waves may extend to partial or non-calcified occlusive material. More particularly, with reference to Figures 22-33, an exemplary and alternative embodiment 1100 comprises an elongate member or carrier 1102, such as a catheter, having a known inflatable angioplasty balloon 1104 attached at or near a distal end 1103 of the elongate carrier 1102, which in certain embodiments may be comprised of laser cut polyimide tubing. The distal end 1105 of the balloon 1104 may be sealed against or around the elongate carrier 1102 to create a watertight barrier, and further comprises a fluid inflation / deflation channel 1106 in fluid communication with the interior of the balloon 1104 and in fluid communication with a fluid-containing reservoir (not shown) located outside the patient, as is known in the art, for inflating and deflating the balloon 1104 with a fluid F. A guidewire lumen (not shown, but known in the art) configured to allow translation of a guidewire extends distally therefrom through the elongate carrier, the location of which is also well known to those skilled in the art.

[0145] It will be appreciated that various embodiments of the present invention are also effective in fluid-filled environments, such as within a body cavity and / or blood vessel, i.e., without the need for a fluid-filled balloon. Although various embodiments are described in connection with a fluid-filled balloon, they also apply to elongate catheters that are placed in a fluid-filled environment, and the flow and pressure wave generators described below may be placed along an elongate carrier in the fluid-filled environment, with or without a sleeve 300. All such embodiments are within the scope of the present invention.

[0146] Thus, at least one flow and pressure wave generator 1200 is provided, each flow and pressure wave generator comprising two conductive features separated by a gap defined between them. In some embodiments, two flow and pressure wave generators 1200, 1200' may be provided. In yet other embodiments, more than one flow and pressure wave generator may be provided, i.e., two or more.

[0147] If a single flow and pressure wave generator 1200 is provided, it may be substantially axially centered within the balloon 1104. In other embodiments, the single flow and pressure wave generator 1200 may be located inside the balloon toward the proximal or distal end.

[0148] When two or more flow and pressure wave generators 1200, 1200' are provided, adjacent flow and pressure wave generators, e.g., 1200, 1200', may be axially spaced apart from one another and the composite gaps defined by each flow and pressure wave generator 1200, 1200' are axially spaced apart from one another. In the case where more than two flow and pressure wave generators are provided, the composite gaps between adjacent subsonic pressure wave generators may be substantially equal or one or more spark gaps may be longer or shorter than for the other flow and pressure wave generators.

[0149] As explained above, a fluid-restricting sleeve 1300 may be provided around one or more of the flow and pressure wave generators 1200, 1200' to help increase the gap between the electrodes in a pair of electrodes.

[0150] 22-33, a first proximal flow and pressure wave generator 1200 may include a proximal electrode 1201 and an axially spaced distal electrode 1202 defining a gap therebetween. A second, more distal flow and pressure wave generator 1200' may then include a proximal ring electrode 1203 and an axially spaced distal ring electrode 1204, also defining a gap therebetween. As will be further described, the distal ring electrode 1202 of the flow and pressure wave generator 1200 and the proximal ring electrode 1203 of the flow and pressure wave generator 200' may be electrically coupled to one another to allow electrical current to pass therebetween.

[0151] For all the embodiments described herein, the saline initially fills the balloon, which acts as a resistive heater, and the applied voltage generates an ionic current that ohmically heats the saline. The saline heats up fastest where the current concentration is greatest. In the case shown, the current concentration is greatest at the electrodes. As explained above, it is also possible to baffle the saline with insulating properties so that the highest current concentration appears at the midpoint between the electrodes. This particular case is interesting both for reducing electrode blast damage and for limiting the volume of saline involved in ionic conduction (reducing heat rejection).

[0152] As will be appreciated by those skilled in the art, the electrical connection may comprise an initial electrical connection to the "high" power side of the voltage pulse generator with the most proximal electrode, or the high power side of the voltage pulse generator with the most distal electrode, or an intermediate electrode located between the proximal and distal electrodes may be connected to the high power side of the voltage pulse generator. First, for example, a proximal electrode electrically connected or electrically coupled to the "high" power side of the circuit and power source to which it is connected, and a distal electrode electrically connected or electrically coupled to the "ground" or "return" side of the circuit and power source to which it is connected. Second, a distal electrode may be electrically connected or electrically coupled to the "high" power side of the circuit and power source, while a proximal electrode may be electrically connected or electrically coupled to the ground or return side of the circuit and power source. Similarly, an intermediately positioned electrode may be electrically connected or electrically coupled to the "high" power side of the circuit and power source, while another electrode may be electrically connected or electrically coupled to the ground or return side of the circuit and power source. In either case, once the flow and pressure wave generator(s) are activated and the arc(s) are generated, a circuit is completed and electrical current flows through the circuit.

[0153] At least one of the flow and pressure wave generators, e.g., 1200, may be in electrical connection and coupling with an externally located power source or power source 1300 directly, which may be configured to provide a voltage pulse of a predetermined intensity and pulse length along the electrical conductor to the proximal ring electrode of the most proximal flow and pressure wave generator 200. Alternatively, the voltage pulse may be delivered without a predetermined intensity or pulse length. In some embodiments, none of them have or require a predetermined voltage or pulse length, and instead a decaying voltage from a collapsing field in an inductor (e.g., the well-known car ignition mechanism) or a capacitor may be employed, with a predetermined level of stored energy dissipated during the pulse in the saline, the cable, the resulting Townsend discharge, the EMI, and the flow.

[0154] Each flow and pressure wave generator 1200, 1200', etc. comprises a pair of spaced apart electrodes. Electrode pairs 1201, 1202, and 1203, 1204 are shown in an axially spaced apart arrangement and are attached, for example by crimping or other attachment means, around the elongate carrier 1102 and immersed in fluid F within the inflatable balloon 1104. Gaps are thus defined between electrode pairs 1201 and 1202, and between electrode pairs 1203 and 1204, and electrodes 1202 and 1203 are in operative electrical communication or connection. As explained above, the gaps may be of equal length or may be configured with different lengths. In some embodiments, a single flow and pressure wave generator 1200 may be provided, whereas in other embodiments, more than one flow and pressure wave generator 1200, 1200', etc. may be provided.

[0155] Thus, in some embodiments, the first and most proximal electrodes 1201 may be electrically connected or in electrical communication with a power source, e.g., power source 1300, configured to provide voltage pulses to the electrode pair(s) comprising the flow and pressure wave generator(s) 1200 via electrical conductors. The most distal electrode, e.g., 1204, may also be electrically connected or in electrical communication with the power source 1300 via a second electrical conductor. The electrodes 1201, 1202, 1203, 1204, including the body B and / or support, may comprise a ring or partial ring shape as shown. Other configurations or shapes of the electrodes or their supports will be apparent to one skilled in the art and are within the scope of the presently described invention.

[0156] The fluid F in the inflatable balloon 1104 is ionically conductive, e.g., saline. The saline is formulated to reduce side effects in the event of balloon rupture, as opposed to other ionically conductive fluids. As explained above, applying a few volts between the spaced apart ring electrodes of each electrode pair 1201, 1202 and 1203, 1204 comprising the flow and pressure wave generators 200 and 200' initiates the flow of ionic current in the saline. Shorted paths between the electrodes experience relatively lower resistance to the flow of ionic current. As the square of the voltage difference divided by the resistance, the locally distributed power varies, and these shorted paths heat up the fastest. Depending on the electrode geometry, the electric field lines connecting the electrodes can pass through as little as a small amount of the saline in the gap between the electrodes, or as much as all of the saline in the balloon. This saline heating step has little or no therapeutic effect, and the priority is to minimize the volume of saline that experiences the electric field from the voltage applied to the electrodes.

[0157] If the applied voltage is sufficient to locally heat the liquid saline to greater than about 350° C., the saline will rapidly boil. For the example flow and pressure wave generator 200, 200′ shown in FIG. 22, the current crowding at the electrodes dictates that boiling will begin in the vicinity of the electrodes. The boiling phase transition causes the involved liquid saline to expand to approximately 1000 times its volume (less if the balloon is pressurized, more if the balloon is below 1 atmosphere). This causes the generation of flows, and the volume occupied by the balloon generally increases as the water vapor expands.

[0158] If the two electrodes of the example flow and pressure wave generator described herein become connected by an adjacent gas path, a different phenomenon emerges. An adjacent gas path can be formed by the spreading of one boiling event or by the joining of bubble fronts from two or more boiling events. The adjacent gas path allows a Townsend discharge to occur. More precisely, if the gas pressure, gap, gas chemistry, and voltage satisfy Paschen's law, the electrons and ions in the gas undergo sufficient acceleration in the electric field during the mean free path between collisions to generate additional ions and electrons in these collisions, generating an ion avalanche capable of carrying very high currents. The initial ion channels connecting the electrodes are called leaders, and once formed, they grow radially rapidly as the ion and electron density (and temperature) increases.

[0159] Prior to the Townsend discharge, the electrical resistance between the electrodes of the flow and pressure wave generator is affected by the ionic conductivity of the saline solution and is typically in the range of 50 Ohms to 50 kilo Ohms. Once the leader is formed and expands radially as far as the voltage generator can support, the resistance between the electrodes drops substantially below 1 Ohm and the current from the power supply becomes overwhelmingly limited by the cabling between the power supply and the flow and pressure wave generator.

[0160] In this manner, when a sufficient voltage generated by the power source 1300 is applied to the most proximal electrode, e.g., 1201, via a conductor in electrical connection or coupling between the power source 1300 and electrode 1201, a current may be passed between electrode 201 and electrode 1202, potentially resulting in a Townsend discharge across the gap defined between electrodes 1201 and 1202. A return conductor in operative electrical connection or coupling with electrode 1202 completes the circuit back to the power source 1300. In this manner, in an embodiment having a single electrode pair with a single flow and pressure wave generator 1200, the circuit resistance may change significantly during a discharge between electrodes 1201 and 1202.

[0161] 22 shows a fluid-filled balloon 1104 in an inflated state with a conductive fluid F, such as saline, filling the interior space of the balloon and spaced apart electrodes 1201, 1202 and 1203, 1204 disposed therein and immersed in the fluid F. The electrodes 1201, 1202, 1203, and 1204 are generally symmetrically disposed around the circumference of the elongate carrier 102 and generally symmetrically disposed along the centerline of the inflatable balloon 1104.

[0162] However, in a preferred embodiment, as shown at least in Figures 27 and 28, a channel or groove 1208 may be defined through or along the electrode along the longitudinal plane to allow the insulated conductor(s) to be at least partially disposed therein to reduce the crossing profile of the system. Thus, the channel 1208 may be formed by cutting out a portion of the electrode, the electrode extending circumferentially around the elongated carrier 1102. Alternatively, as shown at least in Figure 28B, the channel or groove 1208 may comprise a gap or space between two spaced apart ends of the electrode, the electrode extending partially circumferentially around the elongated carrier 1102, and the conductor extending along the outer surface of the elongated carrier 1102. With the exception of the interruption of the channel 208 in the ring electrode(s), the preferred structure is symmetrical as described above, although asymmetric electrode(s) may also be employed.

[0163] 22-33 show possible arrangements and embodiments of the spaced apart electrodes forming each electrode pair and the conductive wires connecting thereto.

[0164] FIG. 223 thus illustrates the elongated carrier 1102, which may comprise laser cut tubing and may be constructed from polyimide or other materials. Two example flow and pressure wave generators 1200, 1200′ are shown in axially spaced apart relationship relative to one another along the elongated carrier 1102. Each flow and pressure wave generator, e.g., 1200, 1200′, includes example spaced apart ring electrodes, 1201, 1202 and 1203, 1204, respectively, each defining a gap between associated spaced apart electrodes of a predetermined length that is the spacing distance between spaced apart electrodes 1201 and 1202, and between 1203 and 1204. A distal electrode, e.g., 1202, of the proximal flow and pressure wave generator 1200 and a proximal electrode 1203 of the distal flow and pressure wave generator 1200' are shown in a relatively close arrangement forming an interface I therebetween, which defines and provides an electrical connection between the two electrodes that define interface I.

[0165] Various forms and types of electrical connections between these intermediate ring electrodes 1202 and 1203 that define interface I are described further herein, but generally comprise a physical or operable electrical connection between the surfaces of the two intermediate electrodes, which may comprise a contact relationship, a weld bead, or a jumper wire or other conductive interconnection element or mechanism between the two intermediate ring electrodes 1202 and 1203, or other conductive connection. Those skilled in the art will readily recognize alternative mechanisms for making the necessary electrical connection between the intermediate electrodes 1202 and 1203, i.e., between adjacent flow and pressure wave generators 1200 and 1200', each of which is within the scope of the present invention. In this arrangement, two or more flow and pressure wave generators 1200, 1200', etc. may be electrically connected in what is effectively a series circuit. The quantity of flow and pressure wave generators used in a particular embodiment may be one, two, or more than two.

[0166] As further described herein, the electrodes described herein are exemplary and other electrode shapes and configurations are within the scope of the present invention. In certain embodiments, and as further described below, at least one electrode of an electrode pair comprising a flow and pressure wave generator may comprise a plurality of aligned points or extensions extending into a gap defined between the electrode pair. This is best illustrated by FIG. 25, in which each electrode 1201 and 1202 comprises a plurality of points or extensions 1201 that are radially aligned with one another and define a plurality of individual gaps capable of generating an arc or spark therebetween. As shown, these multiple individual gaps are distributed around at least a portion of the circumference of the elongate member 1102.

[0167] Furthermore, certain embodiments may comprise a plurality of electrode pairs, with at least one electrode pair comprising a proximal-most electrode in wired or otherwise electrical communication with the power source 1300. In some embodiments, more than one electrode pair in the plurality may comprise a proximal-most electrode in wired or otherwise electrical communication with the power source 1300, with at least one electrode pair in the plurality being separately and individually energized by the power source 1300. Thus, certain embodiments may comprise a parallel connection arrangement of at least some electrode pairs, or may comprise a combination of one or more sets of electrode pairs and serially connected sets of electrode pairs with parallel connections back to the power source.

[0168] Those skilled in the art will recognize that the reference to the most proximal electrode of an electrode pair and an operative electrical connection or coupling with the generator 1300 is merely exemplary. Simply switching an operative electrical connection between the most distal electrode of an electrode pair and the generator 1300 is within the scope of the present invention.

[0169] In certain forms, the individual flow and pressure wave generators 1200, 1200' may be controlled with respect to the strength of the applied voltage, the strength of the current flow that results in an arc between the electrodes comprising the flow and pressure wave generators, the duration of the current flow and arcing between the electrodes comprising the flow and pressure wave generators, the current in the primary side of the discharge inductor, the charge in the discharge capacitor, and / or the initiation time of the current flow and arcing between the electrodes comprising the flow and pressure wave generators.

[0170] Catheters and electrodes

[0171] As provided above, an example laser etched polyimide tube 1102 as shown in FIGS. 24-27 may be provided with ring electrodes 1201, 1202, and 1203, 1204, which are attached to the tube 1102 with insulated wires connecting the electrodes back to an external voltage pulse generator / power supply 1300.

[0172] In the two wire configuration shown, the gap between the electrodes may be shortened by increasing the distance between the two adjacent central, middle electrodes (1202 and 1203) in the electrode pair while electrically connecting the electrodes with additional wires.

[0173] 30A and 30B provide an example ring electrode E having a body portion B defining a central opening A configured to securely engage the catheter 1102, a channel 208, a surface defining a plurality of points 1206, and a flat rear surface. FIG. 30A shows a set of electrode points or extensions 1206 that are not corroded. FIG. 230B provides an electrode point or extension 1206' illustrating the example effect of corrosion at one point due to arcing between adjacent ring electrodes. If corrosion reduces the tendency of the electrode point or extension 1206' to participate in ionization and arcing, one or more of the remaining points 1206 may be engaged to generate an arc across the gap between the electrodes of the electrode pair.

[0174] The electrode points or extensions 1206 may have a substantially triangular profile as shown, but this is merely exemplary. Finally, other profiles are contemplated. The basic function of the electrode points 1206 is to allow the arc to be initiated at different locations on the electrode. Thus, any shape extending away from the body B of the electrode, generally toward the most distal electrode of the electrode pair, which includes the flow and pressure wave generators, and generally toward the spark gap defined therebetween, will suffice. The tip regions of adjacent ones of the electrode points are radially spaced apart from one another in certain embodiments.

[0175] Multiple points on the electrodes, e.g., the example electrodes facing the spark gap region defined between 1201 and 1202, allow electrical breakdown streamers to start from several different positions or points 1206 located on and / or around the electrode body B, so that when some are eroded by the arc, viable electrode points or extensions 1206 remain. This extends the effectiveness and life of the electrode and reduces the voltage required to strike an arc. In addition, since the path of the arc may include debris, arcing originating from different positions, i.e., points 1206, of the electrode(s) body B helps to reduce debris and reduces the likelihood of short circuits forming. In this way, the environment surrounding the electrodes and within the spark gap between them is maintained as uniform as possible during a treatment session with multiple pulses.

[0176] Thus, as shown in the drawings, and as can be readily understood by one of ordinary skill in the art, the non-corroded point(s) 1206 involved in the electric arc begin to corrode as the electric arc progresses. As shown in FIGS. 26 and 30B, the electrode points 206 may corrode and shorten during repeated arcing events, forming degraded or corroded points 1206'. In turn, as can be understood and shown, the spark gap between the corroded or corroded points 1206' may lengthen, creating a longer flow and distance, and resistance, between them. In this way, the current streamer may continually seek a shorter, less resistive spark gap formed or defined by or between one or more non-corroded points 1206 that are longer than the corroded point(s) 1206'. Relatedly, in some embodiments, as best shown in FIG. 24, one or more of the uncorroded points 1206 may have a longer length than one or more other points 1206, as measured by the relative length of extension of the point(s) 1206 toward the spark gap. The longer point(s) 1206 are shortened to define a longer spark gap length therebetween, thus comprising a shorter, less resistive spark gap length than the spark gap length of the shorter other point(s) 1206, or the spark gap length of the corroded point 1206'. FIG. 14 shows one example of a set of points 1206, where one point 1206 is "longer" than an adjacent "shorter" point 1206 and an even shorter point 1206' that has been shortened due to corrosion from electrical arcing. As one skilled in the art can readily appreciate, the current streamers may preferably seek out shorter, less resistive spark gaps, ie, spark gaps with one or more “longer” points 1206 .

[0177] 25 and 26, the extension or point(s) 1206 of an electrode pair, e.g., 1201, 1202, may be configured to define a plurality of spark or arc gaps therebetween, with each spark gap of the plurality corresponding to a pair of opposing extensions or points 206 aligned radially and longitudinally between the spaced apart electrode examples 1201, 1202. In this manner, as one spark gap lengthens due to corrosion as described herein, current streamer formation may migrate to the other pair of longitudinally aligned opposing extensions or points 1206 that are not corroded, thus, in some embodiments, defining a spark gap that is shorter than the spark gap lengthened due to corrosion of the associated opposing extensions or points 1206. Additionally, and as shown, the extensions or points 1206 of an electrode pair, e.g., 1201, 1202, are radially spaced apart from one another around the periphery of the associated electrode 201 and / or 1202. Accordingly, and as described further herein, the corresponding spark gaps therebetween are also radially spaced apart. As a result, a first electric arc across the first spark gap and a corresponding first pressure wave generated by the first electric arc may occur at a first radial location around the electrodes 1201, 1202 and around the elongated member or carrier 1102. A subsequent electric arc and its generated pressure wave may occur at a second radial location around the electrodes 1201, 1202 that is spaced apart from the first radial location.

[0178] The electrodes, including the example electrodes 1201, 1202, 1203, 1204, may be metallic or semiconducting and may be plated with secondary alloys. The base metal may be composed of copper or beryllium copper. The plating may be composed of platinum, gold, tungsten, osmium, silver, titanium, nickel, or other electrochemically less active metals. Carbon surfaces such as graphite, graphene, and diamond may also be used. Additionally, stainless steel and steel alloys may be used.

[0179] The connection between the electrode pairs, e.g., 1201, 1202 and 1203, 1204, may be realized in many embodiments. As described above and shown at least in FIG. 10, in one embodiment, the two intermediate electrodes, e.g., 1202 and 1203, may be placed in a physically contacting relationship, and the electrical connection effectively has a short between the contacting electrodes 1202, 1203, allowing current to flow between them. The electrodes 1201, 1202, 1203, 1204 may have rear surfaces (shown in FIG. 28B) that may be substantially flattened, and the rear surfaces of the intermediate ring electrodes 1202, 1203 may be in physical contact engagement. Alternatively, the rear surfaces of the example intermediate electrodes 1202, 1203 may be spaced apart, as further described herein. Even more alternatively, the rear faces of the intermediate ring electrodes may comprise complementary shapes, e.g., one convex and the other concave, such that one rear face fits within the other, providing a more complete physical contact engagement between the intermediate ring electrodes, e.g., 1202, 1203. The rear faces, which may be relatively flat, comprise opposite sides of a plurality of points 206 that form and define the surface of each example ring electrode 1201, 1202, 1203 and 1204.

[0180] 28, the rear faces of the intermediate electrodes 1202, 1203 may be configured in adjacent but spaced apart, non-contacting engagement, a jumper conductive wire may be disposed between the intermediate electrodes 1202, 1203 across interface I, or a weld bead may interconnect the electrodes 1202, 1203 at interface I. Alternative means of achieving the necessary electrical connection at interface I between the intermediate electrodes 1202, 1203 may occur to one skilled in the art, and each such electrical connection means is within the scope of the present invention.

[0181] Alternative electrode embodiments include at least some non-ring electrodes attached or carried or connected to the elongate catheter 1102, with pairs of non-ring electrodes arranged in a spaced apart configuration to form flow and pressure wave generators as described above in connection with the ring electrode embodiments. Ring and non-ring electrodes may be combined in any system.

[0182] As explained above, a fluid containing sleeve 300 may be provided in any of the flow and pressure wave generators of Figures 22-33 to help provide a longer gap between the electrodes.

[0183] In certain embodiments, selected individual points or extensions 1206 may be specifically energized at individual wired connection(s) for at least a period of time and / or during treatment of a particular region of the target vessel, and / or the individual points 1206 may have their electrical supply stopped to ensure that they are not involved in current flow.

[0184] In other embodiments, the points 1206 may be selectively and intentionally degraded (or not) based on the choice of material and / or the relative length of the tip of a particular point 1206 relative to other points 1206.

[0185] Wire Routing / Cable Routing

[0186] The disposable catheter assembly may include two or more insulated conductors that connect the system of electrodes, electrode pair(s), and / or flow and pressure wave generator(s) to a power source. A typical excitation pulse is 200A@4KV to develop an arc, where the conductor dominates the load, requiring a load impedance of 20 ohms. The round trip cable length for the disposable catheter is approximately 10 feet, with a maximum cable resistance of 1 ohm / foot per trace, which is typical for 40ga copper wire. Additional cable flexibility results from using multiple strands of denser bonded wire with the same cumulative cross-sectional area as 40ga wire.

[0187] The drawing shows electrical conductors with insulators operably connected to a power source 1300, one of the conductors electrically coupled to a proximal-most electrode 1201, an electrical structure well known to those skilled in the art. Figure 27 provides one example of an embodiment of a connection, where an end of the insulated conductor is stripped from the insulation to expose a length of distal conductor portion 1212 that is operably connected to electrode 1201. A similar connection mechanism may be employed for the connection between the other electrical conductor and the distal-most electrode, e.g., element 1204.

[0188] Alternatively, the conductors may include a distal conductor portion 1214 that is stripped from the insulation and connected to the associated ring electrode by a weld bead 1216 as shown in Figure 29. Any of the conductors may be connected to the associated ring electrode in this manner.

[0189] To minimize the outer diameter and crossing profile of the system, the conductors may extend within a lumen defined in the catheter 1102, with the distal conductor portion operably connected to an associated electrode through an opening in the catheter 102 and / or via a weld bead as previously described.

[0190] Alternatively, and as shown in the figures, the electrodes 1201, 1202, 1203, 1204 may include a channel or groove 1208 sized for the conductor(s) to reside therein. The channel 1208 may provide a connection point for one or more electrodes, as shown, for example, in Figures 27 and 28. The channel 1208 may allow the conductor(s) to slide therealong to accommodate changing positions of the catheter 1102 while the example device 1100 is advanced through the patient's vasculature.

[0191] Even more alternatively, a longitudinal channel or a helical or other shaped channel may be defined in the wall of the elongate catheter 1102. The conductor(s) may be disposed at least partially within the channel to help minimize the crossing profile of the system.

[0192] Power supply / pulse generator

[0193] In some embodiments, a capacitor bank may be provided and charged for an example non-conducting period of one minute, followed by shorting or connecting the capacitor to the electrodes for discharge and arcing. The charging period may be less than one minute in preferred embodiments. In other embodiments, a current may be established on the primary side of a transformer, and the current is stopped to create a large voltage across the secondary side.

[0194] As mentioned, pulses may be delivered to the electrodes at least once per second, so the charging period may be significantly shorter than one minute. The pulse repetition rate may be limited by the sensed temperature of the conductive fluid F and / or the balloon material to prevent the temperature of the surrounding tissue from rising above a predefined threshold, e.g., 1° C. for cardiac tissue. The temperature may be monitored using temperature sensors mounted within the conductive fluid F and / or on the inner surface of the balloon, or at other locations along the outer surface of the catheter 102. The temperature sensors may be in operative communication with an externally located processor that is operatively coupled to a predefined thermal threshold(s) and an alarm is generated via a display or other means. In some embodiments, the voltage pulses may be locked out with no further pulses being permitted. In other embodiments, once the predefined thermal threshold is met or exceeded, no further voltage pulses are permitted, but the voltage pulses may continue once the sensed temperature falls below the predefined thermal threshold.

[0195] The capacitor bank may be charged from either direction and the FETs or induced spark gaps are controlled to allow the capacitor bank to discharge between the electrodes in an H-bridge configuration. In some embodiments, the current sign may be configured to be reversed. In some embodiments, phase shaping may be performed to suppress EMI. In some embodiments, both the current and voltage may be monitored to inform what the voltage setting for the next pulse delivery should be. In some embodiments, the voltage may be terminated on a pulse-by-pulse basis, while in other embodiments, the voltage is not terminated on a pulse-by-pulse basis. Similarly, the electrical arc across any set of electrodes comprising the flow and pressure wave generators may be terminated on a pulse-by-pulse basis in some embodiments, while in other embodiments, said electrical arc may not be terminated on a pulse-by-pulse basis.

[0196] Part of the treatment occurs due to the pressure and tension phase of the shock wave propagating through the lesion. The peak pressure scales as the energy stored in the shock wave and (for short length discharges) the inverse cube of the distance from the Townsend discharge to the treatment site. Because the radial distance between the discharge and the treatment site is not precisely controlled, high precision in the control of voltage and current is not necessary. The current may droop or decay exponentially during the pulse, reversing sign between pulses, and ring or oscillate during the pulse. The flow portion of the treatment is optimized by initially deflating the balloon somewhat (to allow it to expand with the evolution of the bubbles) and boiling most of the water, with the time evolution of the flow being tens of microseconds. The pressure portion of the treatment is optimized by applying electrical energy to the Townsend discharge while its impedance is high, a state that lasts tens of nanoseconds.

[0197] The current and voltage output may be monitored for proper operation. Measuring an open or short may generate a prompt or alert to replace the catheter assembly with a new catheter assembly. Monitoring the DC impedance between the electrodes, e.g., 201 and 202, allows the patient to detect and correct catheter insulation leaks. As described further herein, monitoring the DC resistance between the electrodes may provide a temperature monitor. Furthermore, it is further understood that if the blood vessel is successfully opened by the treatment, the resistance of the saline conducting between the electrodes will change.

[0198] Additionally, sensing and / or monitoring the conductivity of the conductive fluid F within the balloon alone or comparing it to the conductivity of a fluid, e.g., blood, outside the balloon provides an alternative mechanism for determining whether the balloon has been damaged, e.g., ruptured or ruptured.

[0199] The patient's heart rhythm may be monitored to ensure that these pulses are synchronized with the inactive phase. The synchronization excludes some standard methods such as a spark gap closing when a capacitor bank reaches a target voltage. In relation, the balloon 104 will inflate and deflate at a specific time and frequency. The voltage pulses may be timed to take advantage of the natural expansion / contraction cycle and frequency. For example, the voltage pulses may be timed for the natural expansion of the balloon and / or the natural contraction of the balloon. The force of the flow and pressure waves impacts the target tissue and / or occlusive material, e.g., calcification, at slightly different angles depending on the balloon's expansion state, especially since the position of the flow and pressure wave generators changes with the balloon's expansion / contraction.

[0200] Temperature Sensor

[0201] As explained above, certain embodiments include small temperature sensors embedded around the electrodes and / or in the conductive fluid F, which may increase the number of treatment pulses up to the limit of a safe increase in tissue temperature, but generally the local tissue temperature should not rise more than about 1° C. Heat diffusion is required 5 mm from the electrodes for heat to be convected by blood circulation. The heat diffusion time for water in a conduit of the relevant radius range is (5 mm)2 / k=167 seconds. However, a 0.5 J pulse will raise a sphere of water of radius 5 mm by about 0.23° C., and the rate of 1 pulse / spark per minute may be increased to 2 pulses / spark per minute in certain embodiments.

[0202] The temperature sensor may be fiber optic based or a micro thermocouple. Because saline increases in conductivity with temperature, the current created by a DC bias applied to the electrodes increases monotonically with temperature, allowing the temperature of the warmest area to be measured directly. As mentioned above, predetermined heat or temperature increase thresholds may be provided with subsequent alerts and / or corrective or remedial actions implemented by programmed instructions implemented by the processor.

[0203] Balloons and inflation fluid

[0204] Angioplasty balloons have been developed and have nuances. An embodiment of the present invention includes a standard angioplasty balloon and the associated basic inflation / deflation mechanisms known in the art. A typical balloon length may be 12 mm and may be used with a 0.14-0.35 inch guidewire. The inflated balloon size may comprise approximately 90% of the nominal vessel size.

[0205] Varying the salinity of the water used to inflate the balloon affects the ionic current density before boiling, with higher saline concentrations lowering the resistance and therefore increasing the power density that can be stored for a given driving voltage. If the ionic current path were allowed to penetrate much of the balloon's interior rather than being restricted to the vicinity of the electrodes, then more current could be consumed to heat a large volume of water without boiling occurring even after a few joules had been dissipated.

[0206] 23, a voltage pulse generated by a power source or voltage pulse generator 1300 comprises a flow and pressure wave generator 1200, e.g., generates streamers in water vapor formed from fluid F interposed between a proximal electrode 1201 and an adjacent, more distal electrode 1202. As described above, the most distal ring electrode is also operatively connected to the power source 1300. Sufficient voltage applied to the proximal electrode 1201 results in streamers, which ultimately produce current flow between the two electrodes of the electrode pair 1201, 1202, generating a resultant flow and pressure wave in the form of an arc and a bubble that propagates through the fluid F. As the bubble shrinks approximately to the point where it rebounds and creates a second growing bubble, the bubble generally collapses, creating another flow and pressure wave.

[0207] We note here that while the pressure waves may travel at sonic and / or supersonic speeds, the flow waves that are generated may travel at subsonic speeds.

[0208] The inter-electrode distance of an electrode pair, e.g., 1201, 1202, may be relatively long, e.g., 5 mm or more, in which case the generated gas bubble and resulting pressure wave may have a cylindrical shape with each end being more spherical in shape.

[0209] The description of the invention and its applications described herein is illustrative and is not intended to limit the scope of the invention. Features of the various embodiments may be combined with other embodiments within the scope of this invention. Variations and modifications of the embodiments disclosed herein are possible, and practical alternatives and equivalents to the various elements of the embodiments may be recognized by those skilled in the art upon studying this patent document. These and other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention.

Claims

1. an elongate member defining a lumen; a first flow and pressure wave generator attached to the elongate member and comprising two spaced apart electrodes; a voltage pulse generator in electrical communication with the first flow and pressure wave generator; an expandable sleeve surrounding the first flow and pressure wave generator, the expandable sleeve having a proximal end and a distal end, the proximal end and the distal end sealed to an outer surface of the elongate member such that fluid within the expandable sleeve in an expanded configuration is restricted to a narrow channel surrounding the two spaced apart electrodes, the expandable sleeve positioned against the insulated outer surface of the first flow and pressure wave generator; a fluid reservoir in fluid communication with the interior of the expandable sleeve; An intravascular lithotripsy system comprising:

2. the expandable sleeve restricts the volume of the fluid to a channel that fills a gap between the two spaced apart electrodes of the first flow and pressure wave generator. The system of claim 1 .

3. the first flow and pressure wave generator comprises three spaced apart electrodes with a first gap between a first electrode and a second electrode and a second gap between the first electrode and a third electrode; the expandable sleeve restricts the volume of the fluid to a channel filling the first gap and the second gap. The system of claim 1 .

4. the gap between the electrodes is in the range of 0.1 mm to 15 mm; The system of claim 2 .

5. The first gap and the second gap are in the range of 0.1 mm to 15 mm. The system of claim 3 .

6. further comprising two spaced apart flow and pressure wave generators; the flow and pressure wave generators are longitudinally spaced apart from one another; The system of claim 1 .

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